Effect of Molecular Architecture and Symmetry on Self-Assembly: A Quantitative Revisit Using Discrete ABA Triblock Copolymers

Abstract

The inherent statistical heterogeneities associated with chain length, composition, and architecture of synthetic block copolymers compromise the quantitative interpretation of their self-assembly process. This study scrutinizes the contribution of molecular architecture on phase behaviors using discrete ABA triblock copolymers with precise chemical structure and uniform chain length. A group of discrete triblock copolymers with varying composition and symmetry were modularly synthesized through a combination of iterative growth methods and efficient coupling reactions. The symmetric ABA triblock copolymers self-assemble into long-range ordered structures with expanded domain spacings and enhanced phase stability, compared with the diblock counterparts snipped at the middle point. By tuning the relative chain length of two end blocks, the molecular asymmetry reduces the packing frustration, and thus increases the order-to-disorder transition temperature and enlarges the domain sizes. This study would serve as a quantitative model system to correlate the experimental observations with the theoretical assessments and to provide quantitative understandings for the relationship between molecular architecture and self-assembly.

Modulation of the Complex Spherical Packings through Rationally Doping a Discrete Homopolymer into a Discrete Block Copolymer: A Quantitative Study

“…37,42,50 With a specifically designed linker consisting of one benzylprotected carboxyl group and three vinyl groups, the linearbranched block copolymers were constructed by consecutively conjugating oDMS and oLA blocks through hydrosilylation and esterification (Scheme S3, see Supporting Information for details). 25,38 In this study, three linear-branched block copolymers with discrete number of repeat units (3S The strong chemical incompatibility between oDMS and oLA blocks drives phase separation at relatively low-molecular weights, 38,42,51 whereas the linear-branched architecture prompts the formation of the unconventional spherical packings. 22,24,25 With a brief thermal treatment (80 °C for 10 min, further annealed at room temperature, ca.…”

“…The strong chemical incompatibility between o DMS and o LA blocks drives phase separation at relatively low-molecular weights, ,, whereas the linear-branched architecture prompts the formation of the unconventional spherical packings. ,, With a brief thermal treatment (80 °C for 10 min, further annealed at room temperature, ca. 25 °C), the nanostructures in the bulk state were analyzed by small-angle X-ray scattering (SAXS).…”

Discrete Diblock Copolymers with Tailored Conformational Asymmetry: A Precise Model Platform to Explore Complex Spherical Phases

“…Discrete polymers with a uniform chain length and a precise chemical structure provide an ideal model system to resolve the phase behaviors with an unprecedentedly high resolution, validating the salient features captured by the theoretical computations. − A few discrete block copolymers have been developed and their phase behaviors have been scrutinized, unraveling intriguing details that have long been covered by molecular weight distribution. ,,− For example, a series of discrete diblock copolymers based on oligo dimethylsiloxane and oligo lactic acid were synthesized through an iterative growth approach by Meijer and co-workers, which self-organized into highly ordered cylinders, gyroids, and lamellae. ,, Johnson et al prepared a small library of stereoisomeric diblock copolymers, demonstrating that it is possible to regulate the self-assembly solely through rational stereochemical manipulations. ,, Our group recently constructed discrete giant polymeric chains using nanometer-sized monomers (i.e., molecular nanoparticles), highlighting the intriguing phase behaviors at a larger length scale. ,, Due to the synthetic challenges, however, the scope of discrete block copolymers and the diversity of the accessible phases are still rather limited . The stepwise synthetic approach can only be applied to certain monomers and is very difficult to reach a high degree of polymerization ( N ).…”

Discrete Giant Polymeric Chain with Precise Sequence and Regio-configuration: A Concise Multiblock Model System

“…In the flexible multiblock block copolymers (for instance, the ABA triblock copolymers), the middle B block could either fold back with two junction points located on the same interface or penetrate through with two junction points distributed on the neighboring interfaces. These two configurations lead to the same lattice dimension and can hardly be discerned. , Moreover, the behaviors of the ABA triblock copolymers are similar to the AB diblock counterparts snipped at the middle point except the enhanced mechanical properties . In this study, the POSS moieties are rigid nanoparticles which have no conformational flexibility .…”

“…44,45 Moreover, the behaviors of the ABA triblock copolymers are similar to the AB diblock counterparts snipped at the middle point except the enhanced mechanical properties. 46 In this study, the POSS moieties are rigid nanoparticles which have no conformational flexibility. 36 This critical difference leads to two unique features: (i) while the zigzag arrangement consists of double-layered domains (comparable to the "loop" config-uration), the parallel packing with a "bridge" configuration can only assume a single-layered packing; (ii) these two arrangements cannot coexist due to size mismatch (Scheme 2).…”